Images overlap posts

I am using a slightly modified version of the theme “Tech 3”.
For whatever reason, any images posted near the bottom of posts run into the next post. This happens both on the main page (http://villagerwithwheel.com) and on individual post pages (http://villagerwithwheel.com/2008/04/elipticals-and-underarmor/).

Am I missing a tag somewhere that this happens? I saw one other similar topic in the forums, but am unsure how to implement it or if it would even help. It talked about vertical height in CSS or something like that.

Also, this doesn’t happen IE (at least 7). This happens in Firefox and Safari (for windows).

Can any help me fix this?

Thanks.